The present invention refers to a holding device for holding an article, which is at least partly manufactured in a thermosetting composite material in connection with heat treatment of said article. The invention also refers to a plant for heat treatment of an article, which is at least partly manufactured in thermosetting composite materials.
It is known to manufacture many articles and construction elements for, for instance, vehicles, ships and aircraft of thermosetting composite materials including fibres, such as glass fibres or carbon fibres. Such composite materials are characterised by a high strength and a relatively small weight. In typical cases, a construction element includes a shell of composite material and a cell core, which may have a honeycomb structure and be enclosed by the shell.
Such a construction element may be manufactured by positioning a not yet set disc, which includes fibres and a plastics, on a holding device with a mould bed of steel or aluminium. Above this disc, a cell core and set edge elements, which includes fibres and a plastics and which surround the cell core, are positioned. On the bed, tool parts or support members, which adjoin the edge element and form a support for the construction element, are mounted. These support members are manufactured in steel or aluminium. Thereafter, a not yet set pre-impregnated laminate, which includes fibres and a plastics, is positioned above the cell core.
Above the support members and the upper disc, a tearing-off cloth or the like is placed and thereafter a substantially close cloth is provided above the tearing-off cloth. The space beneath the close cloth is vacuum pumped and the holding device is introduced into an autoclave, in which the temperature and the pressure are increased successively to desired levels in order to set the construction element. In typical cases, this thermosetting temperature is about 180xc2x0 C. When the thermosetting has been obtained, the holding device is removed from the autoclave and the construction element is dismounted from the holding device.
One problem, which is connected to such a manufacturing of composite articles, is that the mould bed expands due to the raised thermosetting temperature. This means that the support members will have other mutual dimensions at the setting temperature than at the room temperature, at which the article to be set is mounted to the holding device. This problem is especially stressed for relatively large construction elements. In order to solve this problem, the holding device has to be dimensioned in such a way that it has proper dimensions at the thermosetting temperature. Such a dimensioning is time and labour consuming.
The object of the present invention is to remedy the problems described above and to enable a manufacturing of articles of thermosetting composite materials with a high precision. Especially, it is referred to relatively large articles.
This object is obtained by the holding device initially defined, which includes
a base element,
an intermediate element, which rests on the base element, and
at least a support member, which is fixable to the intermediate element and arranged to support said article on the intermediate element during the heat treatment,
wherein the intermediate element is manufactured in a material which has a neglectable thermal expansion at least up to a temperature level, at which the heat treatment is intended to take place, and wherein the intermediate element is displaceably positioned on the base element.
By such an intermediate element, the underlying base element or the bed may be permitted to expand due to a raised temperature during the heat treatment without influencing the position of the support members in relation to each other and to the intermediate element. Consequently, the support members may be positioned very exactly at the positions, which correspond to the shape of article to be manufactured. The holding device according to the invention thus permits a simple manufacturing of articles, which are at least partly manufactured in composite materials.
According to an embodiment of the invention, the intermediate element is at least partly manufactured in a first composite material. Composite materials have a substantially neglectable thermal expansion at least up to a temperature at which the composite material has been set. Such a material, which may be substantially the same as the composite material of the article to be manufactured, is therefore suitable as a carrier of this article and the support members, which define the outer contour of the article. Advantageously, the first composite material includes fibres and a plastic material. Said fibres may for instance include carbon fibres and said plastic material a thermosetting epoxy resin.
According to a further embodiment of the invention, said support member is at least partly manufactured in a material, which has a neglectable thermal expansion at least up to a temperature level at which the heat treatment is intended to take place. In such a way, the shape of the support member or support members may be maintained during the entire manufacturing process and heat treatment, wherein a high dimensional accuracy of the article to be manufactured may be obtained. Advantageously, said support member is thereby at least partly manufactured in a second composite material, which may include fibres and a plastic material, for instance carbon fibres and an epoxy resin. The second composite material may include a higher percentage of plastics than the first composite material and have a lower setting temperature. Said support member may be fixable at the intermediate element by means connecting members, for instance screw connectors.
According to a further embodiment of the invention, the intermediate element has a thickness which is thin in relation to the base element. In such a way, the cost of the holding device according to the invention may be kept at a low level and the previously used bed may substantially be maintained as carrier of the holding device and the article to be manufactured. The base element may at least partly be manufactured in a metal material, for instance including a steel material.
According to a further embodiment of the invention, the holding device includes a flexible, substantially close cloth, which is arranged to be placed over the entire intermediate element, said support member and said article, wherein the holding device includes attachment members arranged to permit closing attachment of the cloth to the base element. Furthermore, the holding device may include means arranged to permit removal of the gas present between the cloth and base element.
The invention is applicable to said article including a shell of composite material and a core enclosed in the shell. Such articles may for instance be used as construction elements in aircrafts, boats and ships, vehicles etc.
The object is also obtained by the initially defined plant, which includes a holding device according to the above description. Advantageously, the plant includes an enclosure, which is arranged to enclose the holding device during the heat treatment, and means for successively increase the temperature and the pressure in the enclosure to said temperature level and a desired pressure level.